1. Field of the Invention
This invention relates generally to an image pick-up tube and, more particularly, is directed to an apparatus for controlling the deflection of an electron beam in an image pick-up tube of the electro-static deflection type.
2. Description of the Prior Art
Generally, in a photoconduction-type image pick-up tube, a cathode electrode emits an electron beam which is directed towards a target electrode having a photo-conversion layer deposited thereon. The image pick-up tube further includes horizontal and vertical deflection plates which, when supplied with appropriate signals, cause the electron beam from the cathode electrode to scan the target electrode. As the electrons from the beam impinge upon the target electrode, some are absorbed thereby to neutralize positive charges that reside there due to incident light from an object image projected on the target electrode. The varying amounts of electron-absorbtion produce an output current of corresponding intensity from which a video output signal is produced.
Generally, although incident light from the object image may be projected on the entire target electrode, the electron beam only scans an effective image area thereon. However, when the area outside of the effective image area on the target electrode is electrically charged due to incident light from the object image, the electron beam does not discharge or neutralize such charges. These unneutralized charges tend to bend or distort the electron beam. Accordingly, the edges of the reproduced picture become distorted.